Continuous impregnating and pulping process



Jan. 12, 1965 DEGASSER C. O. BENNETT ETAL CONTINUOUS IMPREGNATING AND PULPING PROCESS SOAKER 3O Filed Sept. 11, 1961 DI GES TER 4O vINVENTORS CARROLL O. BENNETT SALVATQRE A. GUERRIERI AGENT United States Patent Filed Sept. 11, 1961, Ser. No. 137,121 13 Claims. (Cl. 162-19) The present invention relates to an improved process for pulping cellulosic material such as wood chips or the like.

One of the more specific aspects of the present invention relates to acontinuous process for digesting cellulosic material in an atmosphere of steam.

It is well known to convert wood chips to pulp for use in the manufacture of paper by batch processes. Such batch processes require long cooking periods and necessitate the use of large installations. Furthermore, the labor and utilities costs of batch operation are high. In recent years several continuous processes for pulping cellulosic material have been developed, however, these processes still require relatively long cooking periods and have made little change in the basic pulping process.

Accordingly, a principal object of the present invention is to provide a process for pulping cellulosic material which remedies the above enumerated shortcomings of known processes.

Another object of the present invention is to provide a continuous process for digesting cellulosic material in an atmosphere or steam.

Still another object of the present invention is to provide a continuous process for digesting cellulosic material and leaching digested material in a counter-current washing operation.

A further object of the present invention relates to providing an improved method of transporting degassed material from a degassing zone to an impregnating zone.

A still further object of the present invention resides in high pressure impregnation of degassed cellulosic material with cooking liquor.

Still a further object of the present invention relates to an improved method for conveying impregnated cellulosic material to a digesting zone.

Pulp produced in accordance with the process of the present invention is easy to bleach, and has extremely good mechanical properties. By virtue of the reduced cooking period required, and of emphasis on cellulosic material transportation utilizing fluidized techniques,

damage to the cellulosic fibers is minimized. Furthermore, counter-current washing in accordance with the present invention yields pulp essentially free from cooking liquor, and makes possible the recovery of a more concentrated black liquor than is obtained by known processes.

These and other objects, features and advantages of the present invention will become more obvious from the following description when taken in connection with the accompanying drawing which shows in the single figure thereof, for purposes of illustration only, a schematic layout of suitable apparatus for carrying out the present invention. Although described particularly in relation to the kraft process, it applies with minor modifications to other processes, such as the sulfite process.

Referring now more particularly to the drawing, the major components of the illustrative apparatus include a chip feed hopper 10, a degasser receiving cellulosic material from the hopper It a soaker in which material transported from the degasser 20 is impregnated with cooking liquor, and a digester having an upper digesting zone 41 and a lower leaching zone 42 in which digested or pulped material is subjected to counter-current washing.

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In operation, cellulosic material is fed from hopper 1%) through a star valve 11 or other suitable feeding device to degasser 20. The feed rate is controlled to maintain a level of cellulosic material above the bottom of the degasser 2t).

' Make-up cooking liquor for the system is introduced to the bottom of the degasser 26 via line 21 for a purpose which will become clearer hereinafter. The introduction of liquor is controlled by suitable liquid level control means 22 so as to maintain a liquor level in the degasser beneath the above referred to material level.

Steam at a pressure of from about 15 to 50 p.s.i.g. is introduced via steam line 23 adjacent the top of the de gasser 20 to preheat and degas that portion of the cellulosic material above the liquor level. The cellulosic material is degassed by substituting steam for air held in the pores of the material. The degasser is sequentially vented at suitable intervals of up to 15 minutes by control means (not shown) by closing steam line 23 and opening vent line 24 to remove the air given up by the cellulosic material. While line 24 is illustrated as branching off from steam line 23, it is obvious that these two lines may be separated. Degassing is accomplished by subjecting the cellulosic material to two cycles of steaming and venting while it is above the liquor level in the degasser.

The make-up liquor introduced through line 21 entrains degassed material and transports the same via line 25 and pump 26 to soaker 30. Pump 26 may raise the pressure of the entrained material and liquor mixture to a pressure in the order of 150 to 300 p.s.i.g. during transportation to soaker 30.

The composition of the make-up liquor introduced is preferably adjusted to maintain a suitable concentration of dissolved substances in the circulating liquor.

Soaker 30 is operated under pressure in excess of p.s.i.g., preferably under pressure of 197 p.s.i.g., and includes an impregnating zone in which the cellulose material resides for sufiicient time to enable hot cooking liquor to diituse thoroughly into the material. Soaker Si? is provided with suitable pressure relief means 31.

Excess cooking liquor is drained from the now impregnated material and recycled through lines 32 and 21 to degasser 20. Suitable liquid level control means 33 may be provided to regulate the recycle through line 32 and the liquor level in soaker 30.

Impregnated material is removed from the bottom of the soaker 30 and conveyed to digester 40 by a screw conveyor 34 or other conveyor device. The liquor level in soaker 30 is maintained at a height that enables excess liquor to be drained from the impregnated material during its upward travel in conveyor 34 back into soaker 3G.

The conveyor 34 discharges impregnated material into digesting zone 41 of digester 40. High pressure steam is admitted to digesting zone 41 through steam line 43 to elevate the material to a cooking temperature and to digest the material in an atmosphere of steam. The cellulosic material is rapidly digested as it passes downwardly through the zone 41 in an atmosphere of steam. The rate of material passagethrough digesting zone 41 is regulated so' that the residence time therein is sufiicient to ensure complete digestion of the material.

Digested material or pulp from digesting zone 41 passes into leaching zone 42. In leaching zone 42 the downwardly flowing pulp is subjected to counter-current washing by wash water entering through line 44. The wash water is metered by a suitable flow controller 45. The wash water leaches cooking liquor out of the pulp, and the resulting black liquor is withdrawn through line 46 at an intermediate point in the digester 40, essentially at a juncture of the digesting zone 41 and the leaching zone 42.

Pulp is withdrawn from the bottom of the leaching zone by a screw press 47 or other suitable discharge means. Any excess liquor removed from the pulp is recycled to the leaching zone 42 via line 48 and pump 48. Pulp leaves the screw press 47 through line 49, and may be further treated by a Jordan beater, further countercurrent washing, screening, and subsequent operations of conventional nature.

While in the illustrative embodiment, digesting zone 41 essentially merges directly into leaching zone 42, it is obvious that the present invention is not limited to such unitary structure but encompasses also a more precise or clearly defined separation of the digesting zone from the leaching zone. Additionally, all control devices such as valves, level control means, flow control means, cyclic cooking liquor and in an atmosphere of steam, and removing digested material from said digesting zone.

2. A process for pulping wood chips or the like comprising imnrcgnating wood chips with cooking liquor at a pressure of 150 to 300 p.s.i.g., feeding the impregnated chips through treating apparatus having an upper zone and a lower zone, introducing steam to said upper zone to digest said chips in non-submergence in cooking liquor and in an atmosphere of steam, and leaching the digested chips in said lower zone by supplying washing liquid into the bottom of said lower Zone and by removing black liquor adjacent the top of said lower zone.

3. A process as defined in claim 2, further comprising removing excess liquor from said impregnated chips prior to entrance into said treating apparatus.

4. A process for pulping cellulosic material comprising sequentially steaming and venting said material to degas said material; impregnating the degassed material with cooking liquor at a pressure of 150 to 300 p.s.i.g., essentially continuously feeding the impregnated material into a digesting zone, digesting said impregnated material in non-submergence in cooking liquor and in an atmosphere of steam, and removing digested material from said digesting zone. 7

5. A process for pulping wood chips comprising degassing said chips in a degasser, introducing liquor adjacent the bottom of said degasser to entrain degassed chips, transporting the resulting entrained chips and liquor mixture to an impregnating zone for impregnation are fed from said impregnating zone into said digesting zone by a screw conveyor.

8. A process for pulping cellulosic material comprising feeding said material to a degassing zone at a rate to maintain a level of material within said degassing zone, sequentially steaming and venting said degassing zone to degas said material, introducing liquor to said degassing zone beneath the level of said material, regulating the introduction of liquor to maintain a liquid level below the level of said material, entraining degassed material in said liquor to transport the same to an impregnating zone, impregnating said degassed material with liquor at a pressureof 150 to 300 p.s.i.g., and essentially continuously digesting impregnated material in non-submergence in cooking liquor and in an atmosphere of steam.

9. A process as defined in claim 8, further comprising recycling liquor from said impregnating zone to said degassing zone. i

10. A process as defined in claim 8, wherein said entrained material and said liquor are raised at least partially to the pressure within said impregnating zone during transportation from said degassing zone'to said impregnating zone.

11. A process as defined in claim 8, further comprising adding make-up liquor to said degassing zone to maintain the concentration of dissolved substances in the impregnating liquor within a desired range.

12. A process for pulping cellulosic material comp-rising feeding cellulosic material to a degassing zone, al-

ternately steaming and venting said material for two cycles in said degassing zone to degas said material, introducing cooking liquor into said degassing zone to entrain said degassed material and transporting saidcooking liquor and the material entrained therein to an impregnating zone, impregnating said entrained material with cooking liquor at a pressure of 150 to 300 p.s.i.g., substantially continuously conveying the impregnated material to a digesting zone, elevating the temperature of said impregnated material to a cooking temperature, digesting said material in non-submergence in cooking liquor and in an atmosphere of steam, substantially continuously withdrawing digested'maten'al from said digesting zone, and leaching blackliquor from said digested material Withdrawn from said digesting zone by counter-current washing.

13. A substantially continuous process for pulping cellulosic material comprising feeding cellulosic material to a degassing zone, alternately steaming and venting said material for two cycles in said degassing zone to degas said materiahintroducing cooking liquor into said degassing zone to entrain saidmatcrial, transporting said cooking liquor and the material entrained therein to an impregnating zone, increasing the pressure of said cooking liquor and said entrained material during transportation,

impregnating said entrained material with cooking'liquor at. a pressure of 150 to 300 p.s.i.g.', recycling cooking liquor from said impregnating zone to saiddegassing zone, substantially continuously conveying the impregnated material to a digesting Zone, draining excess cooking liquor from said impregnated material back into said impregnating zone, elevating the temperature of said impregnated material to a cooking temperature, digesting said material in n on-submergence in cooking liquor. and in an atmosphere of steam, substantially continuously withdrawing digested material from said digesting zone, and leaching black liquor from said digested material withdrawn from said digesting zoneby counter-current washing.

1 References Cited in the file of this patent UNITED STATES PATENTS Schandroch Mar. 3, 1959 

1. A PROCESS FOR PULPING CELLULOSIC MATERIAL COMPRISING IMPREGNATING CELLULOSIC MATERIAL WITH A COOKING LIQUOR AT A PRESSURE OF 150 TO 300 P.S.I.G., SUBSTANTIALLY CONTINUOUSLY FEEDING IMPREGNATED MATERIAL INTO A DIGESTING ZONE, DIGESTING SAID IMPREGNATED MATERIAL IN NON-SUBMERGENCE IN COOKING LIQUOR AND IN AN ATMOSPHERE OF STEAM, AND REMOVING DIGESTED MATERIAL FROM SAID DIGESTING ZONE. 